//https://leetcode.cn/problems/01-matrix/

class Solution {
    int dx[4] = { 0,0,-1,1 };
    int dy[4] = { -1,1,0,0 };
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& mat) {
        int m = mat.size(), n = mat[0].size();
        vector<vector<int>> v(m, vector<int>(n, -1));
        queue<pair<int, int>> q;

        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (mat[i][j] == 0)
                {
                    v[i][j] = 0;
                    q.push({ i,j });
                }
            }
        }

        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();


            for (int i = 0; i < 4; i++)
            {
                int x = a + dx[i];
                int y = b + dy[i];

                if (x >= 0 && x < m && y >= 0 && y < n && v[x][y] == -1)
                {
                    v[x][y] = v[a][b] + 1;
                    q.push({ x,y });
                }
            }
        }
        return v;


    }
};